Conventional audio speakers compress/heat and rarify/cool air (thus creating sound waves) using mechanical motion of a cone-shaped membrane at the same frequency as the audio frequency. Most cone speakers convert less than 10% of their electrical input energy into audio energy. These speakers are also bulky in part because large enclosures are used to muffle the sound radiating from the backside of the cone (which is out of phase with the front-facing audio waves). Cone speakers also depend on mechanical resonance; a large “woofer” speaker does not efficiently produce high frequency sounds, and a small “tweeter” speaker does not efficiently produce low frequency sounds.
Thermoacoustic (TA) speakers use heating elements to periodically heat air to produce sound waves. TA speakers do not need large enclosures or depend on mechanical resonance like cone speakers. However, TA speakers are terribly inefficient, converting well under 1% of their electrical input into audio waves.
The present invention relates to an improved transducer (i.e., speaker) that includes an electrically conductive membrane such as, for example, a graphene membrane. In some embodiments, the transducer can be an ultrasonic transducer. An ultrasonic transducer is a device that converts energy into ultrasound (sound waves above the normal range of human hearing). Examples of ultrasound transducers include a piezoelectric transducers that convert electrical energy into sound. Piezoelectric crystals have the property of changing size when a voltage is applied, thus applying an alternating current (AC) across them causes them to oscillate at very high frequencies, thereby producing very high frequency sound waves.
The location at which a transducer focuses the sound can be determined by the active transducer area and shape, the ultrasound frequency, and the sound velocity of the propagation medium. The medium upon which the sound waves are carries can be any gas or liquid (such as air or water, respectively).
Graphene membranes (also otherwise referred to as “graphene drums”) have been manufactured using a process such as disclosed in Lee et al. Science, 2008, 321, 385-388. PCT Patent Appl. No. PCT/US09/59266 (Pinkerton) (the “PCT US09/59266 application”) described tunneling current switch assemblies having graphene drums (with graphene drums generally having a diameter between about 500 nm and about 1500 nm). PCT Patent Appl. No. PCT/US11/55167 (Pinkerton et al.) and PCT Patent Appl. No. PCT/US11/66497 (Everett et al.) further describe switch assemblies having graphene drums. PCT Patent Appl. No. PCT/US11/23618 (Pinkerton) (the “PCT US11/23618 application”) described a graphene-drum pump and engine system.
In embodiments of such graphene-drum pump and engine systems the graphene drum could be between about 500 nm and about 1500 nm in diameter (i.e., around one micron in diameter), such that millions of graphene-drum pumps could fit on one square centimeter of a graphene-drum pump system or graphene-drum engine system. In other embodiments, the graphene drum could be between about 10 μm to about 20 μm in diameter and have a maximum deflection between about 1 μm to about 3 μm (i.e., a maximum deflection that is about 10% of the diameter of the graphene drum). As used herein, “deflection” of the graphene drum is measured relative to the non-deflected graphene drum (i.e., the deflection of a non-deflected graphene drum is zero).
FIG. 1 depicts a perspective view of the graphene-drum pump system illustrated in the PCT US11/23618 application (described in paragraphs [00102]-[00113] and in FIGS. 1-3, therein). FIGS. 2-3 depict close-ups of the graphene-drum pump (in the graphene-drum pump system of FIG. 1) in exhaust mode and intake mode, respectively.
As illustrated in FIGS. 1-3 (which are similar to FIGS. 1-3 of the PCT US11/23618 application), the top layer 102 is graphene. The top layer is mounted on an insulating material 103 (such as silicon dioxide). Graphene-drum pump 101 utilizes a graphene drum as the main diaphragm (main diaphragm graphene drum 201). The main diaphragm seals a boundary of the cavity 202 of the graphene-drum pump 101. The cavity is also bounded by insulating material 103 and a metallic gate 203 (which is a metal such as tungsten). The metallic gate 203 is operatively connected to a voltage source (not shown), such as by a metallic trace 204. The main diaphragm graphene drum 201 can be designed to operate in a manner similar to the graphene drums taught and described in the PCT US09/59266 application and PCT US11/23618 application.
The graphene-drum pump also includes an upstream valve 205 and a downstream valve 206. As illustrated in FIG. 2, upstream valve 205 includes another graphene drum (the upstream valve graphene drum 207). The upstream valve 205 is connected (a) to a fluid source (not shown) by a conduit 208 and (b) to the cavity 202 by conduit 209, which conduits 208 and 209 are operable to allow fluid (such as a gas or a liquid) to flow from the fluid source through the upstream valve 205 and into the cavity 202. The upstream valve 205 also has a cavity 210 bounded (and sealed) by the upstream valve graphene drum 207, the insulating material 103, and upstream valve gate 211. The upstream valve graphene drum 207 can be designed to operate in a manner similar to the graphene drums taught and described in the PCT US09/59266 application and PCT US11/23618 application. For instance, the upstream valve 205 can be closed or opened by varying the voltage between upstream valve graphene drum 207 and upstream valve gate 211. When the upstream valve 205 is closed, van der Waals forces will maintain the upstream valve graphene drum 207 in the seated position, which will keep the upstream valve 205 in the closed position.
As illustrated in FIG. 2, the downstream valve 206 includes another graphene drum (the downstream valve graphene drum 212). The downstream valve 206 is connected (a) to the cavity 202 by a conduit 213 and (b) to a fluid output (not shown) by conduit 214, which conduits 213 and 214 are operable to allow fluid to flow from the cavity 202 through the downstream valve 205 and into the fluid output. The downstream valve 206 also has a cavity 215 bounded (and sealed) by the downstream valve graphene drum 212, the insulating material 103, and downstream valve gate 216. The downstream valve graphene drum 212 can be designed to operate in a manner similar to the graphene drums taught and described in the PCT US09/59266 application and PCT US11/23618 application. For instance, the downstream valve 206 can be closed or opened by varying the voltage between downstream valve graphene drum 212 and downstream valve gate 216. When the downstream valve 206 is closed, van der Waals forces will maintain the downstream valve graphene drum 212 in the seated position, which will keep the downstream valve 206 in the closed position. Generally, upstream valve gate 211 and downstream valve gate 216 are synchronized so that when the upstream valve 205 is opened, downstream valve is closed (and vice versa).
FIG. 2 depicts the graphene-drum pump 101 in exhaust mode. In the exhaust mode, the upstream valve 205 is closed and the downstream valve 206 is opened, while the main diaphragm graphene drum 201 is being pulled downward (such as due to a voltage between the main diaphragm graphene drum 201 and metallic gate 203). This results in the fluid (such as air) being pumped from the cavity 202 through the downstream valve 205 and into the fluid output.
FIG. 3 depicts graphene-drum pump 101 in intake mode. In the intake mode, the upstream valve 205 is opened and the downstream valve 206 is closed, while the main diaphragm graphene drum 201 moves upward. (For instance, by reducing the voltage between the main diaphragm graphene drum 201 and metallic gate 203, the graphene drum 201 will spring upward beyond its “relaxed” position). This results in the fluid (such as air) being drawn from the fluid source through the upstream valve 205 and into the cavity 202.
To reduce or avoid wear of the upstream valve 205 that utilizes an upstream valve graphene drum 207, embodiments of the invention can include an upstream valve element 217 to sense the position between the upstream valve graphene drum 207 and bottom of cavity 210. Likewise to reduce or avoid wear of the downstream valve 206 that utilizes a downstream valve graphene drum 212, embodiments of the invention can include an downstream valve element 218 to sense the position between the downstream valve graphene drum 212 and bottom of cavity 215. The reason for this is because of the wear that upstream valve 205 and downstream valve 206 will incur during cyclic operation, which can be on the order of 100 trillion cycles during the device lifetime. Because of such wear, upstream valve graphene drum 207 and downstream valve graphene drum 212 cannot repeatedly hit down upon the channel openings to conduit 209 and conduit 213, respectively.
As shown in FIG. 2, upstream valve element 217 is shown in the center/bottom of cavity 210 of the upper valve 205, and downstream valve element 218 is shown in the center/bottom of cavity 215 of downstream valve 206. Upstream valve element 217 is used to sense the position of the upstream valve graphene drum 207 relative to the bottom of cavity 210 by using extremely sensitive tunneling currents as feedback. A separate circuit (not shown) is connected between the upstream valve element 217 and the upstream valve graphene drum 207. Likewise downstream valve element 218 is used to sense the position of the downstream valve graphene drum 207 relative to the bottom of cavity 215 by using extremely sensitive tunneling currents as feedback. A separate circuit (not shown) is connected between the upstream valve element 218 and the upstream valve graphene drum 212.
With respect to the upstream valve 205, when the upstream valve graphene drum 207 is within about 1 nm of the upstream valve element 217, a significant tunneling current will flow between the upstream valve graphene drum 205 and the upstream valve element 217. This current can be used as feedback to control the voltage of upstream valve gate 211. When this current is too high, the gate voltage of upstream valve gate 211 will be decreased. And, when this current is too low, the gate voltage of upstream valve gate 211 will be increased (so that the valve stays in its “closed” position, as shown in FIG. 2, until it is instructed to open). There will likely be a gap (around 0.5 nm) between the upstream valve graphene drum 207 and channel opening to conduit 209 when the upstream valve 205 is closed; this gap is so small that it prevents most fluid molecules from passing through the upstream valve 205 yet the gap is large enough to avoid wear. For instance, in an embodiment of the invention, a resistor and voltage source (not shown) can be utilized. The resistor can be placed between the upstream valve element 217 and the voltage source. When the upstream valve graphene drum 207 comes within tunneling current distance (such as around 0.3 to 1 nanometers) of upstream valve element 217, the tunneling current will flow through upstream valve graphene drum 207, upstream valve element 217 and the resistor. This tunneling current in combination with the resistor will lower the voltage between upstream valve element 217 and upstream valve graphene drum 207, thus lowering the electrostatic force between upstream valve element 217 and upstream valve graphene drum 207. If upstream valve graphene drum upstream valve graphene drum moves away from upstream valve graphene 217, the tunneling current will drop and the voltage/force between upstream valve graphene drum 207 and upstream valve element 217 will increase. Thus a 0.3 to 1 nanometer gap between upstream valve graphene drum 207 and upstream valve element 217 is maintained passively which allows the valve to close without causing mechanical wear between upstream valve graphene drum 207 and upstream valve element 217.
With respect to downstream valve 206, downstream valve element 218 can be utilized similarly.
In further embodiments, while not shown, standard silicon elements (such as transistors) can be integrated within or near the insulating material 103 near the respective graphene drums (main diaphragm graphene drum 201, upstream valve graphene drum 207, or downstream valve graphene drum 212) to help control the respective graphene drum and gate set.
FIG. 4 depicts another embodiment of a graphene-drum pump system illustrated in the PCT US11/23618 application (described in paragraphs [00124]-[00127] and in FIG. 7-8, therein). FIG. 5 depicts the graphene-drum pump system of FIG. 4 with the graphene drum in a different position.
In FIGS. 4-5 (which are similar to FIGS. 7-8 of the PCT US11/23618 application), an alternate embodiment of the present invention is shown that locates the graphene drum 201 such that the cavity 202 (in FIG. 2) is separated into two sealed cavities. (The change of position of graphene drum 201 is shown in FIGS. 4-5). Per the orientation of FIGS. 4-5, graphene drum 201 seals an upper cavity 401 and a lower cavity 402. As shown in FIGS. 4-5, upstream valve 205 and the downstream valve 206 are positioned to allow the pumping of fluid in and out of upper cavity 401.
As depicted in FIGS. 4-5, lower cavity 402 is oriented between the graphene drum 201 and the gate 203. Lower cavity 402 can be evacuated to increase the breakdown voltage between the graphene drum 201 and the gate 203. The maximum force (and thus the maximum graphene drum displacement) between the graphene drum 201 and the gate 203 increases as the square of this voltage. Thus, the pumping speed of the device 400 will increase significantly with an increase in the maximum allowable voltage.
As noted above, upper cavity 401 can be filled with air or some other gas/fluid that is being pumped. The vacuum in the lower cavity 402 can be created prior to mounting the graphene drum 201 over the main opening and maintained with a chemical getter. Small channels (not shown) between the lower cavities 402 could be routed to an external vacuum pump to create and maintain the vacuum. A set of dedicated graphene drum pumps mounted in the plurality of graphene drum pumps could also be used to create and maintain vacuum in the lower chambers (since pumping volume is so low these dedicated graphene drum pumps could operate with air in their lower chambers).
Similar to other embodiments shown in the PCT US11/23618 application, in FIGS. 4-5, graphene drum 201 can act like a giant spring: i.e., once the gate 203 pulls graphene down (as shown in FIG. 4), when released the graphene drum 201 will spring upward (as shown in FIG. 5).
FIG. 6 depicts another embodiment of a graphene-drum pump system illustrated in the PCT US11/23618 application (described in paragraphs [00129]-[00131] and in FIG. 9, therein). The graphene-drum pump system 600 shown in FIG. 6 can be actuated without requiring feedback as described above with respect to FIG. 2. In this embodiment, non-conductive member 604 (such as oxide) is placed between the graphene drum 201 and metallic gate 601 so that the graphene drum 201 cannot go into runaway mode and so that graphene drum 201 will not vigorously impact metallic gate 601 when seating. In embodiments of the invention, setting the graphene drum 201 (non-deflected) to metallic gate 901 distance to 20% of the diameter of the graphene drum 201 will prevent runaway (for a maximum deflection that is in the order of 10% of diameter of the graphene drum 201) and will allow the graphene drum 201 to seat softly on a surface of the non-conductive member 604 (such as oxide) without the need for feedback.
As shown in FIG. 6, when the graphene drum 201 is an open position, fluid can flow either (a) in inlet/outlet 602, through cavity 202, and out outlet/inlet 603 or (b) in outlet/inlet 603, through cavity 202, and out inlet/outlet 902 (due to the pressure differential between inlet/outlet 902 and outlet/inlet 903).
As shown in FIG. 6, the metallic gate 601 and metallic trace 605 have a non-conductive member 606 (such as oxide) between them. A voltage source 607 can be placed between the metallic gate 601 and the metallic trace 605 operatively connected to the graphene drum 201. The non-conductive member 604 physically prevents the graphene drum 201 and the metallic gate 601 from coming in contact with one another. This would prevent potentially damaging impacts of the graphene drum 201 and metallic gate 601.
While not illustrated here, in further embodiments of graphene-drum pump systems shown in the PCT US11/23618 application, such systems can be designed to prevent the graphene drum and metallic gate from coming in contact. For instance, the graphene drum could be located at a distance such that its stiffness that precludes the graphene drum from being deflected to the degree necessary for it to come in contact with metallic gate. In such instance, the graphene drum would still need to be located such that it can be in the open position and the closed position. Or, a second and stabilizing system can be included in the embodiment of the invention that is operable for preventing the graphene drum from coming in contact with the gate.
Such embodiments of graphene-drum pump systems illustrated in the PCT US11/23618 application can be used as a pump to displace fluid. As discussed in the PCT US11/23618 application, this includes the use of such embodiments in a speaker, such as a compact audio speaker. While the graphene drums operate in the MHz range (i.e., at least about 1 MHz), the graphene drums can produce kHz audio signal by displacing air from one side and pushing it out the other (and then reversing the direction of the flow of fluid at the audio frequency). Utilizing such an approach: (a) provides the ability to make very low and very high pitch sounds with the same and very compact speaker; (b) provides the ability to make high volume sounds with a very small/light speaker chip; and (c) provides a little graphene speaker that would cool itself with high velocity airflow. Accordingly, these graphene-drum pump systems (of PCT US11/23618 application) solve some of the problems of conventional speakers (such systems are efficient, compact, and can produce sound over the full range of audio frequencies without a loss of sound quality).
However, it has been found that such electrically conductive membrane transducers (of PCT US11/23618 application) have limitations because these systems requires air to flow from the back of the chip/wafer to the front of the chip/wafer. Furthermore, these systems also require the valves to operate properly. Accordingly, there is a need to simplify the design of electrically conductive membrane transducers to reduce their complexity and cost. Furthermore, there is a need to reduce and/or eliminate the contacting and wear of the elements that occurs in these systems of PCT US11/23618 application.
The two main advantages of the current graphene membrane transducer are that it can draw/push air in/out the same vents (allowing everything to be on one side of the chip/wafer if desired) and the system does not require valves to work. These two simplifications result in much lower complexity and cost. Also, there are no contacting/wear elements in the current invention. Since the graphene membrane transducer sends audio waves out from one face of a chip, there is no need to mount the device in a bulky enclosure (the backside of conventional cone speakers must be sealed to stop oppositely phased sound from canceling front-facing sound). If graphene membrane transducers assemblies are mounted on both sides of a chip, it is also possible to cancel reaction forces (by producing sound waves in phase from each side) and thus unwanted vibration.